1. Field of the Invention
The present invention relates to a rotor structure of a claw pole type of actuator of a single phase structure, and more specifically, it relates to a rotor magnet structure and a magnetization pattern of an actuator that is inexpensive, is easy to assemble, and has stable characteristics of repetitive rotational operation.
2. Description of the Prior Arts
In an actuator in which an electric rotating machine of a single phase structure with a claw pole type of structure is provided with a stop mechanism so as to enable a rotor to be repetitively rotatably operated by excitation of a coil, it is desired to increase a dynamic torque while ensuring a detent torque and to increase an angle range of rotational operation.
Conventionally, the following two methods have been proposed on the side of a rotor magnet to increase a dynamic torque while ensuring a detent torque and to increase an angle range of rotational operation.
In the first method, a magnet with magnetic anisotropy is used and a groove or a cut is provided along an axial direction of the magnet in a magnetic pole center portion of one of the poles (e.g., only N pole) so that the magnetic balance between N and S poles may be disturbed to expand an angle range of rotational operation. In the second method, a cylindrical type of rotor magnet is divided into a plurality of parts in the axial direction thereof so that the magnetic poles of the parts are shifted in their peripheral direction, laminated and fixed.
However, the first method has such drawbacks that many steps are required to ensure the precision of the shape of the groove or the cut (specifically, the central angle of the groove or the cut), with the result that processing is complicated. Particularly, in case of a sintered magnet whose outer periphery needs to be ground after sintering, the magnet with such groove or cut on the outer periphery has difficulty to ensure not only the degree of cylindricality but also the stable maintenance of a shape of the groove or the cut. Also, there is a drawback that machining of the groove or the cut causes an increase in cost.
In the second method in which magnets are laminated, it is difficult to perform the work In which a plurality of cylindrical magnets are laminated and fixed in the axial direction thereof while ensuring the concentricity and the appropriate shifted amounts of the magnetic pole peak positions. Assembly work after magnetization has further difficulty caused by repulsion effect between divided magnets (since the magnets should be set to repulse each other for shifted amounts of 20 to 60 degrees of an electrical angle.) and causes unstable shifted amounts.
Thus, it is desired that a rotor magnet is composed, employing a single cylindrical type of magnet in order to compose this type of actuator at a low cost.
The present invention has been attained in view of the aforementioned problems and it is an object of the present invention to provide an actuator of a single phase claw pole structure with a rotor magnet structure which sufficiently ensures detent torque and dynamic torque, has characteristics of wide angle range of rotational operation, is inexpensive, and has stable characteristics, and a magnetization method of the rotor magnet.
In order to solve the above-mentioned problems, an actuator of a single phase structure according to the present invention is characterized in that the rotor magnet comprises a single magnet whose magnetic pole peak position of at least one of N and S poles on the surface thereof shifts stepwise in the axial direction thereof.
According to another aspect of the present invention, a claw pole type of actuator of single phase structure comprises
(a) a stator yoke composed of a pair of substantially circular plane yokes formed of soft magnetic materials, pole teeth which axially protrude from an inner circumferential edge of the respective plane yokes and which are disposed to face each other, extending in an axial direction, and a cylindrical ring provided on an outer circumferential edge of one of said plane yokes;
(b) an armature being constituted by installing a coil formed by winding a magnet wire in a coil receiving section shaped like an annular recess formed by said plane yokes, said pole teeth, and said cylindrical ring of said stator yoke: and
(c) a stator assembly which has flanges with bearings provided on both end surfaces of said armature and in which a rotor provided with a magnet for a magnetic field composed of a permanent magnet being installed to face said pole teeth of said stator with a minute gap provided therebetween; wherein the rotor magnet has a cylindrical shape, and magnetic pole peak positions of at least one of N and S poles thereof shift stepwise in the axial direction thereof.
An actuator according to the present invention is characterized in that the rotor magnet has two distribution patterns of magnetic flux density in the axial direction thereof.
An actuator according to the present invention is characterized in that the rotor magnet is of magnetic anisotropy.
An actuator according to the present invention is characterized in that shifted amounts of the magnetic pole peak positions of N and S poles at axially stepwise different positions on the rotor magnet are equal.
An actuator according to the present invention is characterized in that the shifted amount of the magnetic pole peak positions of the rotor ranges from 20 to 60 degrees in terms of an electrical angle.
An actuator according to the present invention is characterized in that the rotor has two magnetic poles.